pidgin/pidgin

Fix the docs that were broken when the sound api was removed

Update the docs for the sound api removal

Testing Done:
Built libpurple-doc, finch-doc, pidgin-doc, and facebook-doc, verified no errors.

Reviewed at https://reviews.imfreedom.org/r/68/
pidgin3_xml = configure_file(
input : 'pidgin3.xml.in',
output : 'pidgin3.xml',
configuration : version_conf,
install : true,
install_dir : join_paths(get_option('datadir'), 'glade', 'catalogs'))